Transcript NUCLEOTIDES AND NUCLEIC ACIDS 2

NUCLEIC ACIDS
BY
DR. MARYJANE
•Are of two types:
•DNA
•RNA
DEOXYRIBONUCLEIC ACID (DNA)
• DNA is a major component of chromosomes found
primarily in the nucleus, although a small amount is
found in mitochondria and chloroplasts.
• Human DNA consists of 2 strands (chains) of
polynucleotides. Each nucleotide is composed of base,
sugar and phosphate.
• The bases in DNA are: guanine, adenine, cytosine and
thymine
• The sugar is deoxyribose.
• The nucleotides are arranged in chains linked together
by phosphodiester bond between C₅ of deoxyribose of
one nucleotide and C₃ of the next one.
Deoxyribose and ribose sugar
PHOSPHODIESTER BOND
• Is a strong covalent bond between a phosphate
group and 5-carbon ring carbohydrate pentoses.
• In DNA and RNA, the phosphodiester bond is the
linkage between the 3′ carbon atom of one sugar
molecule and the 5′ carbon atom of another with
sugar molecules being deoxyribose in DNA and
ribose in RNA
• The 3′ carbon atom bears the –OH group and the
5′ carbon bears the phosphate group.
PHOSPHODIESTER BOND
CHARGAFF’S PAIRING
• It was found that in DNA molecule:
• a. Adenine is paired with thymine (A=T) by 2
hydrogen bonds.
• b. Guanine is paired only with cytosine (G≡C) by
3 hydrogen bonds.
• Thus in double stranded DNA molecule, the
content of adenine equals that of thymine and
the content of guanine equals that of cytosine.
• Also the G≡C bond (3 hydrogen bonds) is much
more stronger than A=T (2 hydrogen bonds).
DNA ORGANIZATION
• 1. CHROMOSOMES:
• a. these are nucleoproteins formed mainly of DNA
and basic proteins.
• b. In man, they are 46 in number.
• c. they bear genes and act as a functional unit of
heredity.
• d. they are capable of reproducing its physical and
chemical structure through successive cell division.
• 2. CHROMATIN: is the condensed DNA-protein
complex.
• Chromatin consists of:
• i. very long double stranded DNA molecule.
• ii. Histones which are basic proteins
• iii. Protamines
• iv. Small quantity of RNA.
• 3. HISTONES: are small proteins and are positively
charged at physiological pH due to their high
content of lysine and arginine.
• There are 5 major classes of histones: H1, H2A,
H2B, H3 and H4.
• These histones are arranged in structural octamer
units called nucleosomes.
• 4. GENE:can be defined as a region of DNA that
controls a hereditary characteristic
• 5. GENOME: is the total chromosomal (DNA)
content of a cell.
DENATURATION OF DNA
• Involves separation of the double helix of DNA
into single strands when hydrogen bonds
between the bases are disrupted.
• Factors that are responsible for denaturation of
DNA includes: ↑temperature, ↓pH.
• Because there are 3 bonds between G and C but
only 2 between A and T, DNA that contains high
concentration of A and T will denaturate at a
lower temperature than G and C rich DNA.
RIBONUCLEIC ACIDS (RNA)
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There are 3 types of RNA:
a. messenger RNA (mRNA)
b. ribosomal RNA (rRNA)
c. transfer RNA (tRNA)
All RNA molecules are formed in the nucleus
under the control of DNA and the enzyme RNA
polymerase.
• All RNA are formed of one strand only.
• Sugar: ribose
• Bases: adenine, guanine, cytosine and uracil.
• Messenger RNA (mRNA): is a one stranded
nucleic acid and forms about 5% of cellular
RNA.
• It is the most abundant
• FUNCTION: mRNA carries the genetic
information from DNA of the nucleus to the
ribosome.
• Ribosomal RNA (rRNA): is the nucleic acid
present in ribosome.
• It is the largest
• Functions for synthesis of protein
• In the nucleus, it is divided into 2 subunits, a
large subunit (60S or 70S) is the binding site
for tRNA and a small subunit (30S or 40S) is
the binding site for mRNA.
• Transfer RNA (tRNA): transports amino acids
to the ribosome for synthesis of protein.
• It forms 15% of the cellular RNA and the
tiniest.